A D V A N C E I N F O R M A T I O N
read mode, active clock edge, RDY configuration, and
synchronous mode active.
operation, the system must drive CE#, WE#, and CLK
to VIL and OE# to VIH when providing an address, com-
mand, and data. The asynchronous and synchronous
programing operation is independent of the Set Device
Read Mode bit in the Burst Mode Configuration Reg-
ister.
Handshaking Option
The device is equipped with a handshaking feature that
allows the host system to simply monitor the RDY
signal from the device to determine when the initial
word of burst data is ready to be read. The host system
should use the programmable wait state configuration
to set the number of wait states for optimal burst mode
operation. The initial word of burst data is indicated by
the rising edge of RDY after OE# goes low.
The device features an Unlock Bypass mode to facili-
tate faster programming. Once the device enters the
Unlock Bypass mode, only two write cycles are
required to program a word, instead of four.
An erase operation can erase one sector, multiple sec-
tors, or the entire device. Table 8, “Programmable Wait
State Settings,” on page 22 indicates the address
space that each sector occupies. The device address
space is divided into four banks: Banks B and C contain
only 32 Kword sectors, while Banks A and D contain
both 8 Kword boot sectors in addition to 32 Kword sec-
tors. A “bank address” is the address bits required to
uniquely select a bank. Similarly, a “sector address” is
the address bits required to uniquely select a sector.
The presence of the handshaking feature may be veri-
fied by writing the autoselect command sequence to
the device. See “Autoselect Command Sequence” for
details.
For optimal burst mode performance on devices
without the handshaking option, the host system must
set the appropriate number of wait states in the flash
device depending on clock frequency and the presence
of a boundary crossing. See “Set Burst Mode Configu-
ration Register Command Sequence” section on page
21 section for more information. The device will auto-
matically delay RDY and data by one additional clock
cycle when the starting address is odd.
ICC2 in the DC Characteristics table represents the
active current specification for the write mode. The AC
Characteristics section contains timing specification
tables and timing diagrams for write operations.
Accelerated Program Operation
The autoselect function allows the host system to
determine whether the flash device is enabled for
handshaking. See the “Autoselect Command
Sequence” section for more information.
The device offers accelerated program operations
through the ACC function. ACC is primarily intended to
allow faster manufacturing throughput at the factory.
If the system asserts VID on this input, the device auto-
matically enters the aforementioned Unlock Bypass
mode and uses the higher voltage on the input to
reduce the time required for program operations. The
system would use a two-cycle program command
sequence as required by the Unlock Bypass mode.
Removing VID from the ACC input returns the device to
normal operation. Note that sectors must be unlocked
prior to raising ACC to VID. Note that the ACC pin must
not be at VID for operations other than accelerated pro-
gramming, or device damage may result. In addition,
the ACC pin must not be left floating or unconnected;
inconsistent behavior of the device may result.
Simultaneous Read/Write Operations with
Zero Latency
This device is capable of reading data from one bank
of memory while programming or erasing in another
bank of memory. An erase operation may also be sus-
pended to read from or program to another location
within the same bank (except the sector being erased).
Figure 33, “Back-to-Back Read/Write Cycle Timings,”
on page 59 shows how read and write cycles may be
initiated for simultaneous operation with zero latency.
Refer to the DC Characteristics table for
read-while-program and read-while-erase current
specifications.
When at VIL, ACC locks all sectors. ACC should be at
VIH for all other conditions.
Writing Commands/Command Sequences
Autoselect Functions
The device has the capability of performing an asyn-
chronous or synchronous write operation. During a
synchronous write operation, to write a command or
command sequence (which includes programming
data to the device and erasing sectors of memory), the
system must drive AVD# and CE# to VIL, and OE# to
VIH when providing an address to the device, and drive
WE# and CE# to VIL, and OE# to VIH. when writing
commands or data. During an asynchronous write
If the system writes the autoselect command
sequence, the device enters the autoselect mode. The
system can then read autoselect codes from the
internal register (which is separate from the memory
array) on DQ15–DQ0. Autoselect mode may only be
entered and used when in the asynchronous read
mode. Refer to the “Autoselect Command Sequence”
section on page 24 section for more information.
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Am29BDS640G
May 9, 2002
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